FEEDING

Echinoderms are heterotrophs and have several methods of feeding. Some are carnivores while others are herbivores. Carnivores use their tube feet to pry open the shells of bivalve mollusks such as clams and scallops. Once the shell has been broken open, the starfish flips its somach out of its mouth, pours out enzymes, and digests its prey in the prey's own shell. After the sea stars haave finished eating, it removes its stomach from the shell and moves it back into his mouth. Sea stars usually eat snails, corals, and even other echinoderms. Some echinoderms are also herbivores, such as sea urchins, scrape algae from rocks by using their 5-part jaw. Sea lilies, basket stars, and some brittle stars, use tube feet on flexible arms to capture plankton that float by on ocean currents. This method of feeding is called filter feeding. The last method is the detritus feeders. The move as a large suction and pick up half sand and detritus. Later, they will digest organic materials and excrete the sand grains.

HABITAT AND ADAPTATIONS

Echinoderms live in marine habitats, although they can occasionally survive being washed up and dried on shore. Within marine habitats, Echinoderms can survive in a wide variety of places. Sea Stars and sea cucumbers, for instance, prefer rocky areas while others often reside in sandy areas where they can bury themselves. Some Echinoderms even use other animals as homes such as the skin of other fish. In order to stay concealed during the day, Echinoderms have adapted to match the colour of their surroundings. Also, to protect and structure their bodies, Echinoderms such as sea urchins have interlocking plates of Calcium Carbonate which form a very hard internal skeleton. Others, such as sea stars and brittle stars have slightly more flexible internal skeletons to allow them to flex and bend their arms. Sea cucumbers have barely any Calcium Carbonate, resulting in a very flexible body containing only remnants of a sturdy internal skeleton. Anther adaptation the Echinoderms have is that they can regenerate body parts. This means that if, for example, a sea star's leg gets cut off by a predator, over time it can form a new one.

DIGESTION

When an echinoderm ingests food, the first step on the path it takes is the mouth, which is on the bottom of the organism. After the mouth, the food travels through the esophagus and into one of the two stomachs of an echinoderm; the cardiac stomach. Some echinoderms can actually take their cardiac stomachs outside of their body. For example, starfish open a bivalve with their strong water-vascular system and push their stomachs inside to digest their prey. Next, the food travels into the pyloric stomach where it is continued to be digested. The last steps of digestion take place in the intestine and digestive glands. Waste is then excreted through the anus.

CONNECTIONS TO OTHER PHYLA

Echinodermata is a very unique phyla in that its organisms live in marine habitats only. Organisms belonging to crustecea, a subphylum of arthropoda, also live in water only, but can be found in fresh water as well as salt water. Other phylums that are strictly aquatic are cnidaria and porifera, but once again these organisms can be found in fresh water and marine habitats. However the phyla with the most similar habitat characertistics is mollusca.
Organisms of the phyla echinodermata all have penta radial symetry, similarly to this cnidarians have radial symetry. Another characteristic they hold is thier endoskeleton, certain members of phyla mollusca also share this characteristic, such as the squid.
A similar function between annelids and echinoderms is that they both have specialized segments of the body. Echinoderms all have an intersection like center, where a majority of their internal organs are found. Annelids too have a specialized first few segments that carry their eyes or antennae. Both starfishes and sea stars from echinodermata have a similar function to octopus's from the phyla mollusca. Both these organisms have suction like appendages, though they are not controlled by the same kind of system their suction like charactaristics make them comparable.

IMPORTANT VOCABULARY

View this link to read some interesting vocabulary about echinoderms: Once link has appeared, click on MOLLUSKS VOCAB ONLY (it is actually echinoderms vocabulary):
http://www.google.com/search?sourceid=navclient&ie=UTF-8&rls=GGLG,GGLG:2005-24,GGLG:en&q=vocab+on+echinoderms

INTERESTING FACTS

Some sea cucumbers have the ability to bring all of their internal mass out of their body to scare away predators. Sea stars are able to regenerate their arms when bitten by a preditor and in some case the whole body has been able to be regenerated from a single arm. The cushion star (top right) releases huge amounts of mucus when threatened by an enemy.